For the beef, heat a deep-fat fryer to 190C, or heat the oil for deep-frying in a deep heavy-based frying pan until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Toss the beef strips in the vegetable oil. In a pestle and mortar, crush the Sichuan peppercorns to a fine powder. Place them in large bowl with the lime and orange zest and cornflour then toss well to combine. Add the beef and toss to coat each piece thoroughly.
In batches, drop the beef into the deep-fat fryer and cook for 2 minutes. Drain on a plate lined with kitchen paper.
For the sauce, heat a frying pan or wok until hot, add the sugar, rice wine and rice wine vinegar and bring to the boil. Add the chillies, chilli flakes, ginger, lemongrass and lime leaves then cook for 5-8 minutes until thickened, sticky and glossy looking.
Add the fried beef to the sauce, remove from the heat and toss well so that all the beef is coated in the sticky sauce.
For the noodles, heat the vegetable oil in a wok over a high heat. When the oil is smoking, add the ginger, garlic and spring onions and stir fry for 2-3 minutes, or until softened. Add the cooked noodles and stir fry for a further minute, or until warmed through. Add the sesame oil, soy sauce, rice wine vinegar and lemon juice and mix well to combine. Add the sesame seeds and stir fry for a further 1-2 minutes. Sprinkle over the coriander and stir well to combine.
To serve, divide the noodles between serving bowls and top with the chilli beef. Place the broccoli in a separate serving bowl.